Y1 Module

Since 2004, our international group began to work on low-cost passive
modular robots. The Y1 modular robot with one DOF in Fig. 1, was
designed by our project cooperator Ph.D.
Juan González-Gómez in 2004 as the first prototype. Using this
prototype, the minimal configurations for movement are studied. Then two
eight-module robots were built for further research purposes. One is a
pitch-connecting modular robot and the other a pitch-yaw connecting
robot, as shown in Fig.2.

Using docking blots, the modules can connect or disconnect easily and
flexibly. Each joint actuated by a RC servo is controlled by means of a
sinusoidal oscillator with four parameters: amplitude, frequency, phase
and offset.

The Y1 module is made of plastic so that the stiffness of its mechanical
structure is quite low. The module breaks very easily since all of tits
mechanical parts are glued together without any professional connecting
components.

Fig .1 Y1 Module

Fig. 2. PYP Configuration.JPG

In Fig. 3, all the prototypes built using Y1 have the electronic and
power supply outside. The electronic part consists of an 8-bit
microcontroller that supplies the Pulse Width Modulation (PWM) signals
to the servos. The robots are connected to a PC by a serial port.

Fig. 3. Controlling the Y1 Module

The control of our modular robot is based on sinusoidal generators to
produce rhythmic motion. From the biological point of view, these
generators act like the Central Pattern Generators (CPGs) located in the
spinal cord of the animals to control variation of the rotation angle
of each module.

The sinusoidal generators produce very smooth movements and have the
advantage of making the controller much simpler. Our model is described
by the following equation (1). Where yi is the rotation angle of the
corresponding module; Ai is the amplitude; T is the control period; t is
time; ?i is the phase; Oi is the initial offset.

Fig. 4 Control Method

Fig. 4 shows a sketch map of the control algorithm. Eight sinusoidal
generators are represented to actuate all modules to rotate. According
to the connecting relationship of the modules, they are divided into
horizontal and vertical groups, which are described as Hi and Vi
respectively. Where i means the module number; ??V is the phase
difference between two adjacent vertical modules; ??H is the phase
difference between two adjacent horizontal modules; ??HV is the phase
difference between two adjacent horizontal and vertical modules.